Merge infra and k3 into one directory again

Since I don't have multiple terraform steps anymore it simply doesn't
make sense to me anymore to split all tasks into separate folders.
Instead I try to be as clear as possible in the README to make it easy
to follow the structure in the future without too much headache.

roles/server-setup/templates/ip-masquerade.sh.j2

@@ -0,0 +1,4 @@
+#!/bin/bash
+echo 1 > /proc/sys/net/ipv4/ip_forward
+iptables -t nat -A POSTROUTING -s {{network_cidr}} -o eth0 -j MASQUERADE
+